A well-received magnetic key operated mechanism used in conjunction with a door lock is that described in U.S. Pat. No. 4,133,194 owned by Bruce S. Sedley, the owner and assignee of the present application. In the patented door lock, a magnetic card key operates a conventional cylindrical door lock with substantially no modification required of the lock, in that a housing for the door lock contains magnetically operated elements mounted on the conventional spindle of the lockset. In use, a properly coded card key is inserted into a slot in the outer rim of the door knob which effects interconnection between the door knob with a conventional driver bar for opening the lockset parts.
Although the patented device is satisfactory for most purposes, several disadvantages in use make improvement desirable. First of all, it is necessary to hold the card in the slot of the doorknob while turning the knob to keep the unlocking mechanism engaged. Furthermore, the necessary diameter of the knob used in the patented device is substantially larger than that of most door knobs which makes rotation awkward when a short backset is used. The latter aspect makes the patented device somewhat impractical for narrow stile doors of the aluminum and glass type which often utilize very short backsets.
Still further, the patented apparatus was designed contemplating mainly doorknob-type locksets and therefore could not easily be adapted for lever or handle operation now being specified in many construction projects to meet handicapped person codes.